Humanin is an AD resilience factor through its interaction with APOE4 Alzheimer?s disease (AD) is a devastating condition affecting millions and costing hundreds of billions of dollars in caregiving expenses, for which no effective therapy exists. The pathophysiology of AD is complex and not fully understood, but the APOE4 genetic variant is the strongest determinant of AD risk. Some APOE4 carriers are nonetheless resilient to AD well into old age. How these high-risk individuals remain dementia-free is an enigma. Mitochondria have been linked to neurodegeneration on many levels, however, their DNA has not been carefully studied in the context of Alzheimer?s disease risk. Our lab characterized humanin, a mitochondrial-derived peptide encoded from the 16S rRNA region of the mtDNA, which has been shown to be a potent neuroprotective factor. Our work shows that humanin administration prevents age-dependent cognitive decline in mice, and others have shown that it slows the progression of amyloid ?-driven neurodegeneration in AD mouse models. In recent unpublished data presented in this grant, we show that humanin directly binds APOE with a preference for APOE4 and attenuates APOE degradation. We have further demonstrated that humanin levels in plasma and CSF are dramatically different depending on the APOE genotype. Separately, we recently identified a SNP in the humanin ORF that is associated with lower humanin levels and with more rapid cognitive decline in individuals followed in the Health and Retirement Study (HRS). Our central hypothesis in this grant is that humanin is an APOE4 resilience factor whose levels and genetic determinants favorably modulate the risk of AD, as a result of its direct binding and stabilization of APOE4. We assembled an interdisciplinary team to examine this hypothesis. We will assess whether humanin genetic variants modify AD risk in APOE4 carriers in three large public databases: HRS, the Wellderly cohort, and ADNI. We hypothesize that the favorable humanin SNP is more common in resilient APOE4 positive individuals. Using Biacore and crystallography approaches, we will identify the structural and functional consequences of humanin/APOE interaction and characterize humanin analogues that protect against APOE4 signaling and proteolysis and the consequences of this phenomenon in neuronal AD cell models in vitro. We will determine whether humanin analogues improve cognition and brain pathology in APOE4-driven AD mouse models and cross humanin-transgenic and humanin-knockdown mice with APOE4 TR mice hypothesizing improved or worsened cognition respectively. Together, this project will engage an interdisciplinary team of scientists to address the significance of humanin?s interactions with APOE and determine, using three independent approaches (well characterized large human databases, sophisticated in vitro methodologies, and state-of-the-art mouse models) and evaluate the therapeutic potential of humanin analogues in Alzheimer?s Disease.